1. Field of the Invention
The present invention relates to an organic light-emitting compound, an organic electroluminescent (EL) device using the compound, and a method of manufacturing the organic EL device, and more particularly, to an organic light-emitting compound that contains a cis-diarylethene group linked with an aliphatic ring, which prevent crystallization of the organic light-emitting compound, and thus is highly soluble to organic solvents and easily provides liquid formulation with organic solvents, an organic EL device using the compound, and a method of manufacturing the organic EL device.
2. Description of the Related Art
Electroluminescent (EL) devices are self-emitting devices which have a wide viewing angle, excellent contrast, and quick response time. EL devices can be classified into inorganic EL devices which use inorganic compounds for emissive layers and organic EL devices which use organic compounds for emissive layers. Compared to inorganic EL devices, organic EL devices have superior luminance, lower turn-on voltage, and quicker response time, and can realize multicolor images.
A typical organic EL device has a stacked structure in the form of an anode/organic emissive layer/cathode structure. Organic EL devices can also have an anode/hole injection layer (HIL)/hole transport layer (HTL)/emissive layer/electron transport layer (ETL)/electron injection layer (EIL)/cathode structure, or an anode/HIL/HTL/emissive layer/hole blocking layer/ETL/EIL/cathode structure.
Materials used in organic EL devices can be classified into vacuum deposition materials and solution coating materials. Vacuum deposition materials should be able to have a vapor pressure of 10−6 torr or higher below 500° C. and may be small molecular materials having a molecular weight of 1200 or less. Solution coating materials should have sufficient solubility and typically include aromatic compounds or heterocyclic compounds.
Manufacturing organic EL devices using vacuum deposition increases costs due to the use of a vacuum system. In addition, when a shadow mask is used to define pixels for natural color display, manufacturing high-resolution pixels is difficult.
On the other hand, manufacturing organic EL devices using solution coating methods such as inkjet printing, screen printing, and spin coating is easy, costs less, and can accomplish a relatively higher resolution than using a shadow mask. However, in terms of thermostability and color purity, blue light emitting molecules which are compatible with solution coating methods are inferior to materials that are compatible with vacuum deposition methods. Also, even when the features are superior, as crystallization occurs after manufacturing, crystals which become as large as the wavelengths of visible light disperse visible light and cause white residue. In addition, pin holes are likely to be formed and deteriorate the devices.
Accordingly, efforts have been made to overcome the limits of the conventional methods and materials and provide a material and an organic EL device which have improved features. However, a satisfactory solution has not yet been obtained.
Thus, a novel small molecular material having improved solubility that is compatible with solution coating methods, and an organic EL device which can be easily manufactured and has a higher resolution using a solution coating method, and which has high thermal stability and color purity due to the use of the small molecular material, are required.